The use of Fe (OH).sub.2 in scrubbing coke oven gas to remove the impurities therefrom is disclosed, for example, in U.S. Pat. Nos. 961,763 (Falding) and 3,021,189 (Mancke), the Fe(OH).sub.2 being a product of a reaction between FeSO.sub.4, NH.sub.3, and water. The processes disclosed in the Falding and Mancke et al patents produce a gas which is relatively clean (the gas leaving the reactor in the Mancke system is said to contain 5 grains of ammonia per 100 cu. feet 60 grains hydrogen sulfide per 100 cu. feet, and 10 grains of hydrogen cyanide per 100 cu. feet). It is noted that the Falding patent refers to the recovery of "values" from the process disclosed therein and specific reference is made to the recovery of ammonium and iron salts.
With the increasing demand for cleaner coke oven gas and an increasing emphasis on abatement and control of process-related pollution, the processes disclosed in the patents referred to are not satisfactory from all standpoints. For example, residual amounts of hydrogen cyanide and hydrogen sulfide still remain in the fuel gas and these, and other impurities, tend to corrode the plant equipment and cause pollution when the gas is utilized. In addition, the production of the reagents used, the scrubbing of the fuel gas, and the production of marketable by-products are all themselves sources of environmental pollution. Further, prior art processes are, in general, incompatible with, that is, do not accept, tar-laden coke-oven gas. Finally, and more generally, prior art processes require multiple gas washing equipment, complex gas handling procedures having high energy requirements, and, as alluded to above, are highly subject to the corrosive influences of the impurities that these processes are designed to remove. However, the features and advantages of the process of the present invention can perhaps be best appreciated by specifically considering these features and advantages.